1. Field of the Invention
The present invention relates to an automatic release timing control system for use with a press which is adapted for producing a release control signal which causes a cooperating feeder to temporarily release the gripping of a sheet material at a proper timing, when pilot pins provided for accurately positioning the sheet material are inserted into pilot holes in the sheet material.
2. Description of the Prior Art
In a conventional press, a feeder for feeding a web of sheet material to the press, for example an independent NC feeder, is provided with an air-actuated release mechanism to temporarily release the gripping of the sheet material. The release mechanism generally includes an air solenoid valve and repeats cyclic operations in which, when the air solenoid valve receives a sheet release signal from a control circuit, the release mechanism effects a releasing operation to temporarily release the sheet material, so that pilot pins of the press can be accurately led into pilot holes in the sheet material. When the pilot pins are inserted into the pilot holes, a press working is performed, and thereafter, when a sheet grip signal is fed from the control circuit to the solenoid valve, the release mechanism terminates the releasing operation and grips the sheet material to feed the same to the press.
In such a conventional release mechanism for the feeder which repeats the cycle of releasing and gripping operation, the release and grip timings are constant, irrespective of the number of revolutions of the press, so that, when the revolution speed of the press is high, the allowable release time becomes short. Because of this fact along with the response time of the release mechanism, it becomes difficult for the release mechanism to follow up the working speed of the press.